Vehicle sensor calibration target alignment system

ABSTRACT

A target alignment system for calibrating a safety sensor mounted on a vehicle with front and rear wheels by locating an optimum target position upon a horizontal surface for accurate calibration of the sensor. The target alignment system comprises a plurality of visual guide projectors and a pair of target assemblies which project a visible guide line perimeter around the vehicle, the perimeter including parallel longitudinal lines on either side of the vehicle, a lateral alignment guide line crossing the longitudinal lines in front of the vehicle, and a center guide line colinear with the vehicle center line. The front and rear wheels of the vehicle are longitudinally aligned causing the vehicle thrust line to match the vehicle center line. One of the visual guide projectors projects a transverse line across the center guide line, creating an intersection point which marks the optimum target position.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of non-provisional patent applicationNo. 17/012,296 filed in the United States Patent Office on Sep. 4, 2020,claims priority therefrom, and is expressly incorporated herein byreference in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to an apparatus and method forcalibrating a vehicle-mounted sensor. More particularly, the presentdisclosure relates to a target alignment system for placing acalibration target and aligning a vehicle's wheels.

BACKGROUND

Automated Driver Assisted Safety Systems (ADAS) increase car and roadsafety by detecting obstacles and mitigating driver error. For example,collision avoidance systems use radar, LIDAR, cameras, or other sensingdevices to scan for obstacles ahead of a vehicle in order to prevent thevehicle from colliding with these obstacles in the event of drivererror. For ADAS systems to function correctly, each of these sensorsmust be accurately calibrated. Furthermore, a vehicle's steering andsuspension must be correctly aligned. For example, a properly calibratedcollision avoidance system is able to accurately locate obstacles andpredict the path of the vehicle as it travels, based on the steeringangle of the wheels, and the speed of the vehicle. Improperly calibratedsensors may cause the ADAS system to miscalculate the true path of thevehicle or the distance between the vehicle and the obstacles, resultingin the ADAS system failing to detect potential collisions.

However, conventional calibration systems and methods have several keydisadvantages. ADAS systems are typically calibrated by placing vehicleson a specialized flat surface, such as a level floor free ofirregularities, with precisely positioned calibration markings whichcannot easily be moved or adjusted. Sensors, such as cameras and radars,are calibrated by placing specialized targets within sensing range alongthe vehicle's center line, with the assumption made that the vehicle'sthrust angle will match the vehicle's center line. Conventional systemsrequire dedicated floor space which cannot easily be used for otherpurposes, thus making them impractical for use in small or crowdedservice facilities. Permanently affixed markings on the floor can alsobe damaged or obscured. Furthermore, standard methods for determiningthe vehicle's centerline, such as by suspending plumb bob from an emblemat the front or rear of the vehicle, are often imprecise. Due to thehigh speed of vehicles and the need to accurately detect obstacles whenthey are far ahead of the vehicle, even small degree of misalignment ofan ADAS sensor may result in serious miscalculations. Lastly,conventional systems often utilize complex devices which are timeconsuming and labor intensive to set up and dismantle.

As a result, there is an urgent need for an improved, easy to use targetalignment system which is capable of accurately determining a vehicle'scenterline and ensuring the thrust angle matches the centerline,locating the optimum position for the placing sensor calibrationtargets, and adapting to irregularities on shop floors or othersurfaces.

In the present disclosure, where a document, act or item of knowledge isreferred to or discussed, this reference or discussion is not anadmission that the document, act or item of knowledge or any combinationthereof was at the priority date, publicly available, known to thepublic, part of common general knowledge or otherwise constitutes priorart under the applicable statutory provisions; or is known to berelevant to an attempt to solve any problem with which the presentdisclosure is concerned.

While certain aspects of conventional technologies have been discussedto facilitate the present disclosure, no technical aspects aredisclaimed and it is contemplated that the claims may encompass one ormore of the conventional technical aspects discussed herein.

BRIEF SUMMARY

An aspect of an example embodiment in the present disclosure is toprovide an apparatus for assisting in calibrating a vehicle safetysensor by precisely locating an optimum target position for accuratecalibration of the sensor. Accordingly, the present disclosure providesa target alignment system which produces a visible guide line perimeteraround a vehicle, including a center guide line which passes centrallyand longitudinally through the vehicle. The optimum target position isthen located along the center guide line and marked by intersecting thecenter guide with a transverse guide line, allowing the calibrationtarget to be accurately placed.

It is another aspect of an example embodiment in the present disclosureto provide a target alignment system which allows the visible guide lineperimeter to be accurately and quickly deployed on any substantiallyflat horizontal surface. Accordingly, the target alignment systemcomprises a plurality of wheel-mounted visual guide line projectors, apair of target assemblies, a lateral guide line projector, a centerguide line projector, a distance measuring projector, a thrust linetarget, and a transverse visual guide projector. The wheel-mountedvisual guides project a pair of longitudinal guide lines upon thehorizonal surface along the sides of the vehicle. Each of the targetassemblies is positioned upon the horizonal surface ahead of the vehicleand is aligned with one of the longitudinal guide lines. The lateralguide line projector projects a lateral guide line upon the horizonalsurface which is perpendicular to the longitudinal guide lines andlaterally aligns the two target assemblies. The distance measuringprojector projects a distance measuring line between the targetassemblies which determines the distance between the longitudinal guidelines. The thrust line target is placed upon the horizontal surfaceintersecting the distance measuring line at a midpoint which isequidistant between the longitudinal guide lines. The center guide lineprojector is aligned with the thrust line target and projects the centerguide line upon the horizontal surface which is colinear with thevehicle center line. The transverse guide line projector is positionedalong one of the longitudinal guide lines at a point marking acalibration distance, to project the transverse guide line whichperpendicularly intersects the center guide line to mark the optimumtarget position.

It is yet another aspect of an example embodiment in the presentdisclosure to provide a target alignment system which allows a thrustline of the vehicle to be matched with the vehicle center line.Accordingly, one of the wheel-mounted visual guide line projectors isattached to each of the front wheels. Each of the front wheels islongitudinally aligned with the corresponding rear wheel, when thelongitudinal guide lines associated with the front and rear wheels forma colinear convergence upon the horizontal surface. Once the front andrear wheels on either side of the vehicle are longitudinally aligned,the resulting thrust line is located between the longitudinal guidelines and is colinear with the vehicle center line.

The present disclosure addresses at least one of the foregoingdisadvantages. However, it is contemplated that the present disclosuremay prove useful in addressing other problems and deficiencies in anumber of technical areas. Therefore, the claims should not necessarilybe construed as limited to addressing any of the particular problems ordeficiencies discussed hereinabove. To the accomplishment of the above,this disclosure may be embodied in the form illustrated in theaccompanying drawings. Attention is called to the fact, however, thatthe drawings are illustrative only. Variations are contemplated as beingpart of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like elements are depicted by like reference numerals.The drawings are briefly described as follows.

FIG. 1A is a diagrammatical top view depicting a target alignment systemwhich produces a visible guide line perimeter to optimally place acalibration target for calibrating a vehicle-mounted sensor, inaccordance with an embodiment in the present disclosure.

FIG. 1B is a diagrammatical top view of a vehicle, depicting the frontwheels being set to a steering angle of zero degrees using a steeringangle sensor, in accordance with an embodiment in the presentdisclosure.

FIG. 2 is a diagrammatical rear perspective view of the vehicle, showinga conventional method for locating a center line using a plumb bobattached to the vehicle rear, in accordance with an embodiment in thepresent disclosure.

FIG. 3 is a diagrammatical side view of a wheel attachment assemblywhich is removably attached to one of the vehicle's wheels and mounts avisual guide projector, in accordance with an embodiment in the presentdisclosure.

FIG. 4 is a diagrammatical top view of the vehicle positioned on ahorizontal surface, depicting longitudinal guide lines projected uponthe horizontal surface by the visual guide projectors attached to eachof the wheels in accordance with an embodiment in the presentdisclosure.

FIG. 5 is a diagrammatical perspective view of a first target assemblyhaving a target plate, and longitudinal and lateral target alignmenttracks, in accordance with an embodiment in the present disclosure.

FIG. 6 is a diagrammatical top view of the first target assemblypositioned alongside a second target assembly, showing the first andsecond target assemblies aligned with the first and second longitudinalguide lines, in accordance with an embodiment in the present disclosure.

FIG. 7A is a diagrammatical perspective view of the first and secondtarget assemblies, showing the longitudinal target alignment tracks ofthe first and second target assemblies aligned with the firstlongitudinal guide line and the second longitudinal guide linerespectively, further showing the first and second longitudinal guidelines reflected on the target plates of the target assemblies, inaccordance with an embodiment in the present disclosure.

FIG. 7B is a diagrammatical perspective view of the first and secondtarget assemblies, showing mis-aligned horizontal level guide linesreflected on the target plates, in accordance with an embodiment in thepresent disclosure.

FIG. 8 is a diagrammatical perspective view of the second targetassembly, showing a lateral alignment visual guide projector positionedperpendicularly to the second longitudinal guide line, in accordancewith an embodiment in the present disclosure.

FIG. 9 is a diagrammatical top view of the target alignment system,showing the alignment visual guide projector emitting an alignment guideline towards the first target assembly for ensuring that the first andsecond target assemblies are equidistant in relation to the vehicle, inaccordance with an embodiment in the present disclosure.

FIG. 10 is a diagrammatical perspective view of the first targetassembly, showing a distance measuring projector positioned upon thefirst target assembly which projects a distance measuring lineperpendicularly to the first longitudinal guide line, in accordance withan embodiment in the present disclosure.

FIG. 11 is a diagrammatical top view of the target alignment system,showing the distance between the first and second longitudinal guidelines being determined using a distance measuring projector, inaccordance with an embodiment in the present disclosure.

FIG. 12 is a diagrammatical perspective view of a thrust line targetwith a thrust line distance target, a thrust target lateral alignmenttrack, and a center guide line alignment mark, in accordance with anembodiment in the present disclosure.

FIG. 13 is a diagrammatical top view of the target alignment system,showing the thrust line target placed upon the horizontal surfacebetween the first and second target assemblies such that the thrust linedistance target intersects the distance measuring line at a distancemeasuring line midpoint and the thrust line target lateral alignmenttrack is aligned with the alignment guide line, in accordance with anembodiment in the present disclosure.

FIG. 14 is a diagrammatical top view of the target alignment system,showing a center visual guide projector which projects a center guideline in alignment with the center guide alignment mark of the thrustline target, in accordance with an embodiment in the present disclosure.

FIG. 15 is a diagrammatical top view of the target alignment system,showing the center guide line as being colinear with the center line ofthe vehicle as determined using the plumb bob, in accordance with anembodiment in the present disclosure.

FIG. 16 is a diagrammatical top view of the target alignment system,showing a starting reference point and an ending reference point beingmeasured along the first longitudinal guide line to mark the calibrationdistance, in accordance with an embodiment in the present disclosure.

FIG. 17 is a diagrammatical top view of the target alignment system,showing a transverse visual guide projector positioned at the endingreference point, which projects a transverse line perpendicular to thefirst longitudinal guide line. The transverse line intersects the centerguide line, and the intersection corresponds to the optimum targetplacement point, in accordance with an embodiment in the presentdisclosure.

FIG. 18 is a diagrammatical top view of the calibration targetpositioned upon the optimum target placement point, in accordance withan embodiment in the present disclosure.

FIG. 19 is a block diagram depicting a calibration error resulting froman incorrectly positioned calibration target, in accordance with anembodiment in the present disclosure.

FIG. 20A is a diagrammatical top view of the target alignment systembeing used to locate a rear optimum target position behind the vehicle,in accordance with an embodiment in the present disclosure.

FIG. 20B is a diagrammatical front view of a calibrated back-up camerasystem, in accordance with an embodiment in the present disclosure.

The present disclosure now will be described more fully hereinafter withreference to the accompanying drawings, which show various exampleembodiments. However, the present disclosure may be embodied in manydifferent forms and should not be construed as limited to the exampleembodiments set forth herein. Rather, these example embodiments areprovided so that the present disclosure is thorough, complete and fullyconveys the scope of the present disclosure to those skilled in the art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1A-B illustrate a target alignment system 10 for calibrating asensor 94 mounted on a vehicle 80. In a preferred embodiment, the sensor94 is a safety device used in an Automated Driver Assisted Safety system(ADAS), such as a camera, or a radar or LIDAR sensing device. The sensor94 is calibrated using a calibration target 109. The vehicle 80 is aconventional wheeled vehicle, such as an automobile or truck, having avehicle front 81F, a vehicle rear 81R, a vehicle left side 82L, avehicle right side 82R, a pair of front wheels 84, and a pair of rearwheels 85. Where the vehicle 80 has four wheels, the front wheels 84comprise a first front wheel 84L and a second front wheel 84R, while therear wheels 85 comprise a first rear wheel 85L and a second rear wheel85R. The target alignment system 10 operates while the vehicle 80 ispositioned upon a horizontal surface 100, such as the ground or a floor.In order for the sensor 94 to be calibrated correctly during a testing,diagnostic, or maintenance procedure, the sensor must be placed at anoptimum target position 72 upon the horizontal surface 100. The targetalignment system 10 allows a user to quickly and accurately locate theoptimum target position 72. Furthermore, the target alignment system 10allows the user to identify and compensate for irregularities in thehorizontal surface 100 which may otherwise interfere with the successfulcalibration of the sensor 94.

Referring to FIG. 2 while continuing to refer to FIGS. 1A-B, the optimumtarget position 72 is located along a vehicle center line 92, and isseparated from the vehicle 80 or other starting reference point 51Athereon by a calibration distance 51. The length of the calibrationdistance 51 is dependent upon the characteristics of the sensor 94. Forexample, the length of the calibration distance 51 may be found withindocumentation provided by the manufacturer of the sensor 94 or thevehicle 80, and may correspond to a reference distance around which thecalibration or diagnostic procedures for the sensor 94 are performed.For example, the documentation for the sensor 94 may dictate that thecalibration target 109 be separated from the sensor 94 or anotherreference point on the vehicle, such as a bumper or wheel axle, by nomore than three meters. The vehicle center line 92 runs longitudinallythrough the vehicle 80 and may be equidistant between the first frontand first rear wheels 84L, 85L and the second front and second rearwheels 84R, 85R. A conventional but imprecise method for locating thevehicle center line involves suspending a plumb bob 93 from an emblem83R located at the vehicle rear 81R, such that the plumb bob 93 hangsabove the horizontal surface 100.

The target alignment system 10 comprises a plurality of wheel-mountedvisual guide projectors, a pair of target assemblies 40, a center visualguide projector, a lateral alignment visual guide projector 34, and atransverse visual guide projector 38. The target alignment system 10 mayadditionally comprise a distance measuring projector 36. Thewheel-mounted visual guide projectors are detachably mounted to thefront wheels 84 and rear wheels 85 of the vehicle 80. In a preferredembodiment, the wheel-mounted visual guide projectors include a firstfront visual guide projector 30A which attaches to the first front wheel84L, a second front visual guide projector 30B which attaches to thesecond front wheel 84R, a first rear visual guide projector whichattaches to the first rear wheel 85L, and a second rear visual guideprojector which attaches to the second rear wheel 85R. Each of thevisual guide projectors is adapted to project a visible line upon otherobjects, such as the horizontal surface 100. These visible lines allowthe user to position and align the components of the target alignmentsystem 10 in order to locate the optimum target position 72 upon thehorizontal surface. Each visual guide projector incorporates a linelaser, rotating laser, or other similar device which projects a beamcapable of producing visible lines.

In order to accurately locate the optimum target position 72, the frontwheels 84 of the vehicle 80 must be adjusted such that front wheels 84and the rear wheels 85 are aligned and the thrust line 50 of the vehicle80 matches the vehicle center line 92. This can be achieved in part byusing a vehicle steering sensor 110 to ensure that the steering angle isset to zero degrees, as well as through other techniques which will beapparent to a person of ordinary skill in the art in the field of theinvention. In addition to steering angle, there are other factors whichaffect the thrust line 50. For example, any variations in wheelalignment due to camber or front or rear toe angle should be corrected,and vehicle ride height and tire pressures should be adjusted toappropriate specifications to assist the calibration procedure. When thefront wheels 84 are aligned with their corresponding rear wheels 85, thethrust line 50 of the vehicle 80 should correspond to the vehicle centerline 92.

The visible lines projected by the first and second front visual guideprojectors form longitudinal guide lines 52 which are oriented inparallel and extend in a forward direction past the vehicle front 81F.In a preferred embodiment, the first front visual guide projector 30Aprojects a first longitudinal guide line 52L while the second frontvisual guide projector 30B projects a second longitudinal guide line52R.

The target assemblies 40 comprise a first target assembly 40L and asecond target assembly 40R. The first and second target assemblies 40L,40R are positioned upon the horizontal surface 100 ahead of the vehiclefront 81F, and are aligned with the first and second longitudinal guidelines 52L, 52R respectively. The lateral alignment guide visualprojector 34 is adapted to project a lateral alignment guide line 58which is perpendicular to the first and second longitudinal guide lines52L, 52R and extends between the first and second target assemblies 40L,40R. The center visual guide projector 32 is placed at a positionbetween the first and second target assemblies 40L, 40R, and projects acenter guide line 70 upon the horizontal surface 100 that is colinearwith the vehicle center line 92. The transverse visual guide projector38 is placed forward of the vehicle front 81F, and is adapted to projecta transverse guide line 56 upon the horizontal surface 100 whichperpendicularly intersects the center guide line 70. The placement ofthe transverse guide line 56 is determined by the calibration distance51, and the resulting intersection between the transverse line 56 andthe center guide line 70 corresponds to the optimum target position 72.The calibration target 109 is placed upon the optimum target position72, thus allowing the sensor 94 to be accurately calibrated.

Turning now to FIG. 3 while also referring to FIGS. 1A-B, each wheel hasa circular wheel rim 86, a tire 87 which surrounds the wheel rim 86, anda wheel center 88. Each wheel-mounted visual guide projector 30 isdetachably secured to one of the wheels via a wheel attachment assembly20. The wheel attachment assembly 20 further ensures that thewheel-mounted visual guide 30 is aligned with the wheel center 88. Inone embodiment, each wheel attachment assembly 20 has a centralconnecting member 23 and a plurality of rim grips 22 attached to thecentral connecting member 23. The rim grips 22 are adapted to grip thewheel at a plurality of points along the circumference of the wheel rim86, between the wheel rim 86 and the tire 87. Each wheel attachmentassembly 20 also has a visual guide attachment point 24 which isconnected to the central connecting member 23 and is adapted to supportone of the wheel-mounted visual guide projectors 30 such that thewheel-mounted visual guide projector 30 is aligned with the wheel center88. In one embodiment, the visual guide attachment point 24 has a pivotplate 25A upon which the wheel-mounted visual guide projector 30 rests.The pivot plate 25A is capable of rotating to ensure that the pivotplate 25A and the wheel-mounted visual guide projector 30 are level withthe horizontal surface 100.

Referring to FIG. 4 while also referring to FIGS. 1A-B and FIG. 3, oncethe first and second front visual guide projectors 30A, 30B have beenattached to the first and second front wheels 84L, 84R, and the firstand second rear visual guide projectors 30C, 30D have been attached tothe first and second rear wheels 85L, 85R, the wheel-mounted visualguide projectors 30 are activated. The first and second rear visualguide projectors 30C, 30D each project a first rear longitudinal guideline 54L and a second rear longitudinal guide line 54R respectively.When the front and rear wheels 84, 85 are longitudinally aligned, thefirst longitudinal guide line 52L and first rear longitudinal guide line54L will form a first convergence 55L, while the second longitudinalguide line 52R and second rear longitudinal guide line 54R will form asecond convergence 55R, thus indicating that the front and rear wheels84, 85 are longitudinally aligned. However, if the steering angle of thefront wheels 84 do not match the steering angles of the correspondingrear wheels 85, the longitudinal guide lines 52 and the rearlongitudinal guide lines 54 will not converge, thus indicating thatfurther adjustment is required. In a preferred embodiment, the visibleguide lines projected by the first and second rear visual guideprojectors 30C, 30D are of a second color, while the visible guide linesprojected by first and second front visual guide projectors 30A, 30B areof a first color, thus allowing the visible guide lines to be visuallydistinguishable by the user.

Turning now to FIG. 5 and FIG. 6 while also referring to FIGS. 1A-B andFIG. 3, once the front and rear wheels 84, 85 are longitudinallyaligned, the target assemblies 40 are positioned upon the horizontalsurface 100 forward of the vehicle front 81F. Each target assembly 40has a target plate 42 which is oriented perpendicularly in relation thehorizonal surface 100. The target plate 42 is substantially planar inshape, and has a target face 42F which is oriented towards the vehiclefront 81F. In one embodiment, each target assembly 40 has a base 48which supports it upon the horizontal surface 100, and supportingportion 44 which extends upwardly from the base 48 and to which thetarget plate 42 is attached. The supporting portion 44 may also allowthe target plate 42 to be alternately raised or lowered in relation tothe base 48. In a preferred embodiment, the base 48 has an adjustableleveling mechanism, such as a plurality of legs 48L, which allow thebase 48 to remain level and a parallel to the horizontal surface 100.Each target assembly 40 also has a longitudinal target alignment track46 which allows the user to longitudinally align the target assembly 40with one of the longitudinal guide lines 52 or rear longitudinal guidelines 54. The longitudinal target alignment track 46 forms a line,groove, ridge, or other similar mark or protrusion upon the targetassembly 40 which allows the user to visually determine when one of thevisible beams is colinear with the track, thus indicating alignment.

Referring to FIG. 8 while also referring to FIGS. 1A-B and FIGS. 5-6,the longitudinal target alignment track 46 of each target assembly 40may have a horizontal component 46H, as well as a vertical component46V. The horizontal component 46H extends horizontally andperpendicularly away from the target face 42F, while the verticalcomponent 46V extends upwardly and perpendicularly away from thehorizontal surface 100. In one embodiment, the horizontal component 46Hextends along the base 48, while the vertical component 46V extendsupwardly along the supporting portion 44.

For each target assembly 40 to be correctly positioned upon thehorizonal surface 100, the longitudinal alignment tracks 46 of the firstand second target assemblies 40L, 40R must be aligned with the first andsecond longitudinal guide lines 52L, 52R respectively. The user mayadjust the target assembly 40 upon the horizontal surface 100 until thelongitudinal alignment track 46 is visibly colinear with the first orsecond longitudinal guide line 52L, 52R as appropriate.

Returning to FIG. 1A while also referring to FIGS. 7A-7B, in a preferredembodiment, the first and second longitudinal guide lines 52L, 52R andthe first and second rear longitudinal guide lines 54L, 54R are producedusing a moving laser, such as a rotating laser, line laser, or othersimilar device within each of the wheel-mounted visual guide projectors30. The moving laser produces a beam that moves along a simulatedvertical plane. Where the vertical plane intersects with the horizontalsurface 100, a visible guide line is produced which corresponds to oneof the longitudinal guide lines 52 or rear longitudinal guide lines 54.Similarly, where the vertical plane intersects with a vertical portionof one of the target assemblies 40 or other vertically oriented object,such as the vertical component 46V of the longitudinal track 46 or thetarget face 42F, a vertical guide line is produced. The first frontvisual guide projector 30A and second front visual guide projector 30Beach project a first vertical guide line 52LV and a second verticalguide line 52RV respectively, while the first rear visual guideprojector 30C and second rear visual guide projector 30D each project afirst rear vertical guide line 54LV and a second rear vertical guideline 54RV respectively.

Referring to FIG. 1A, FIG. 4, FIG. 6, and FIGS. 7A-B, the use of thehorizontal and vertical components 46H, 46V of the longitudinal targetalignment track 46 increases the precision of alignment between thelongitudinal guide lines 52 and the target assemblies 40. The firstlongitudinal guide line 52L and the first rear longitudinal guide line54L first align upon the horizontal surface 100 and form the firstconvergence 55L. The colinear first longitudinal guide line 52L and thefirst rear longitudinal guide line 54L continue to extend forwardly tothe first target assembly 40L to align with the horizontal component 46Hof the longitudinal target alignment track 46, while the first verticalguide line 52LV and first rear vertical guide line 54LV vertically alignwith the vertical component 46V. As the horizontal component 46H isperpendicular to the target face 42F, correct longitudinal alignmentensures that the target face 42F is perpendicular to the firstlongitudinal guide line 52L and the first rear longitudinal guide line54L. The vertical alignment of the first vertical guide line 52LV andthe first rear vertical guide line 54LV with the vertical component 46Vfurther ensures that the first target assembly 40L is correctly leveledupon the horizontal surface 100 and that the supporting portion 44points directly upward.

Similarly, the principles disclosed above regarding the longitudinal andvertical alignment of the first target assembly 40L can be applied tothe precision alignment of the second target assembly 40R by aligningthe second longitudinal guide line 52R and the second rear longitudinalguide line 54R with the horizontal component 46H of the longitudinaltarget alignment track 46, and aligning the second vertical guide line52RV and the second rear vertical guide line 54RV with the verticalcomponent 46V.

Furthermore, in a preferred embodiment, each of the wheel-mounted visualguide projectors 30 is also adapted to project a moving laser that moveswithin a simulated horizontal plane via a rotating laser, cross-linelaser, or similar means. When the simulated horizontal plane intersectswith an object, such as one of the target faces 42F, a visiblehorizontal guide line is produced. The first front visual guide lineprojector 30A projects a first horizontal guide line 52LH, the secondfront visual guide line projector 30B projects a second horizonal guideline 52RH, the first rear visual guide line projector 30C projects afirst rear horizontal guide line 54LH, while the second rear visualguide line projector 30D projects a second rear horizontal guide line54RH.

Referring to FIGS. 1A-B, FIG. 3, FIG. 7B, and FIG. 9, the firsthorizontal guide line 52LH and the first rear horizontal guide line 54LHare visible upon the target face 42F of the first target assembly 40L,while the second horizontal guide line 52RH and the second rearhorizontal guide line 54RH are visible upon the target face 42F of thesecond target assembly 40R. In a preferred embodiment, the simulatedhorizontal planes projected by each of the wheel-mounted visual guideprojectors 30 each pass through the wheel center 88 of their respectivewheels. For example, the second front visual guide projector 30B can beadjusted using the wheel attachment assembly 20 until the secondhorizontal guide line 52RH passes through the wheel center 88 of thesecond front wheel 84R. The target faces 42F of the first and secondtarget assemblies 40L, 40R are utilized to determine whether the frontand rear wheels 84, 85 are level upon the horizontal surface 100.

Where the horizontal surface 100 is free of irregularities, the firsthorizontal guide line 52LH and the first rear horizontal guide line 54LHwill be horizontally aligned upon the target face 42F of the firsttarget assembly 40L, while the second horizontal guide line 52RH and thesecond rear horizontal guide line 54RH will be horizontally aligned uponthe target face 42F of the second target assembly 40R. If one of thehorizontal guide lines appears to be lower upon its associated targetface 42F than the other horizontal guide line due to an irregularitypresent upon the horizontal surface 100, the user may raise theassociated front or rear wheel to restore horizonal guide lines tohorizontal alignment. For example, if the second rear wheel 85R is lowerthan the second front wheel 84R due to a depression in the horizontalsurface 100 below the second rear wheel 85R, the user may raise thesecond rear wheel 85R by inserting a shim plate 113, wedge, or otherdevice between the second rear wheel 85R and the horizontal surface 100to restore the horizontal alignment between the second rear horizontalguide line 54RH and the second horizontal guide line 52RH upon thetarget face 42F of the second target assembly 40R.

In a preferred embodiment, each of the wheel-mounted visual guideprojectors 30 has a self-leveling mechanism which ensures that thesimulated horizontal plane is level, and that the simulated verticalplane is perpendicular to the simulated horizontal plane.

Turning to FIG. 9 while also referring to FIG. 5 and FIG. 8, to enableaccurate calibration of the sensor 94, the first and second targetassemblies 40L, 40R must be laterally aligned upon the horizontalsurface 100 to ensure that the target faces 42F of both targetassemblies 40 are equidistant in relation to the sensor 94. In apreferred embodiment, the lateral alignment visual guide projector 34 isadapted to project a lateral alignment guide line 58 upon the horizontalsurface 100 which extends between the first and second target assemblies40L, 40R. Each target assembly 40 may have a lateral alignment track 47,which is oriented perpendicularly to the longitudinal target alignmenttrack 46. When the target assemblies 40 are placed upon the horizontalsurface 100, the lateral alignment track 47 of the first and secondtarget assemblies 40L, 40R are inwardly oriented such that each lateralalignment track 47 faces towards the opposite target assembly 40. Thelateral alignment visual guide projector 34 may be placed upon eitherthe first or the second target assembly 40L, 40R, with the projectingend 31 directed towards the opposite target assembly 40. The lateralalignment guide line 58 aligns with the lateral target alignment track47 of the target assembly 40 from which the lateral alignment guide line58 is projected, and the lateral alignment guide line 58 extends towardsthe lateral target alignment track 47 of the opposite target assembly40. Where necessary, one or both of the target assemblies 40 areadjusted upon the horizontal surface 100 until the lateral targetalignment track 47 of the opposite target assembly 40 and the lateralalignment guide line 58 are aligned.

In a preferred embodiment, the lateral alignment visual guide projector34 is placed upon the base 48 of one of the target assemblies 40, withthe projecting end 31 of the lateral alignment visual guide projector 34oriented towards the other target assembly 40. In the examples shown inFIGS. 5, 8, and 9, the lateral alignment visual guide projector 34 maybe placed upon the base 48 of the second target assembly 40R inalignment with the lateral target alignment track 47 thereof, and thelateral alignment guide line 58 is projected across the horizontalsurface 100 to intersect with the first target assembly 40L and alignwith its lateral target alignment track 47. Note however, that thelateral alignment visual guide projector 34 may alternatively bepositioned upon the first target assembly 40L, so that the lateralalignment guide line 58 intersects with the second target assembly 40Rto align with its lateral target alignment track 47.

In a preferred embodiment, the lateral target alignment track 47 has ahorizontal component 47H and a vertical component 47V, in a mannersimilar to the longitudinal target alignment track 46. In a preferredembodiment, the vertical component 47V of the lateral target alignmenttrack 47 is positioned upon the supporting portion 44 of the targetassembly 40, while the horizontal component 47H is positioned upon thebase 48 and extends perpendicularly away from the vertical component47V.

The lateral alignment visual guide projector 34 may also be adapted toproject a simulated vertical plane by means of a rotating laser or othersimilar device. In addition to producing a lateral alignment guide line58 upon the horizontal surface 100, the horizontal component 47H of thelateral target alignment track 47, or any other horizontally disposedobject or surface, the simulated vertical plane also produces a lateralalignment guide line vertical portion 58V upon intersecting with avertically disposed object such as the vertical component 47V of thelateral target alignment track 47. By aligning the lateral alignmentguide line vertical portion 58V with the lateral target alignmentguide's 47 vertical portion 46V, the user can ensure that the verticalportions 46V of both target assemblies 40 are in vertical alignment. Ina preferred embodiment, the alignment of the lateral alignment guideline vertical portion 58V with the vertical portion 46V of the lateraltarget alignment track 47 ensures that the base 48 of the targetassembly 40 is level with the horizontal surface 100 and that thesupporting portion 44 points directly upward. This can be used inconjunction with the vertical alignment of the first and secondlongitudinal guide lines 52L, 52R with the vertical portions 46V of thelongitudinal target alignment tracks 46 to ensure greater precision.

Referring to FIG. 10, FIG. 11, and FIG. 12 while also referring to FIG.1A, once the first and second target assemblies 40L, 40R are laterallyaligned with each other and longitudinally aligned with the first andsecond longitudinal guide lines 52L, 52R, a visible guide line perimeter12 is formed. The visible guide line perimeter 12 extends from the firstrear visual guide line projector 30C to the first target assembly 40Lvia the first longitudinal guide line 52L and the first rearlongitudinal guide line 54L, then from the first target assembly 40L tothe second target assembly 40R via the lateral alignment guide line 58,and finally from the second target assembly 40R to the second rearvisual guide projector 30D via the second longitudinal guide line 52Rand the second rear longitudinal guide line 54R. The visible guide lineperimeter 12 is precisely aligned and allows for the center guide line70 and the transfer guide line 56 to be placed in order to locate theoptimum target position 72.

In order to place the center visual guide projector 32, a distancebetween the first and second longitudinal lines 52L, 52R must bemeasured. In a preferred embodiment, a distance measuring projector 36,such as a laser rangefinder, is placed on either the first or secondtarget assemblies 40L, 40R. A corresponding distance target 42D ispositioned upon the opposite target assembly 40. The distance measuringprojector 36 projects a distance measuring line 53 to the distancetarget 42D to determine the distance between the first and secondlongitudinal guide lines 52L, 52R. In the example illustrated, thedistance measuring projector 36 may be placed upon the base 48 of thefirst target assembly 40L, while the distance target 42D is positionedupon the second target assembly 40R, in alignment with the secondlongitudinal guide line 52R.

Referring to FIG. 12, FIG. 13, and FIG. 1A, a thrust line target 60 isused to identify a distance measuring line midpoint 53M which isequidistant between the first and second longitudinal guide lines 52L,52R, by dividing the distance therebetween in half. In a preferredembodiment, the thrust line target 60 has a thrust line target lateralalignment track 64, and a center line alignment mark 68 orientedperpendicularly thereto. The thrust line target 60 also has a thrustline distance target 62 which is longitudinally aligned with the centerline alignment mark 68. The thrust line target 60 is positioned upon thehorizontal surface 100 such that the lateral alignment guide line 58aligns with the thrust line target lateral alignment track 64, and thethrust line distance target 62 intersects the distance measuring line53. In one embodiment, the thrust line target 60 has a thrust linetarget base 66 which rests upon the horizontal surface 100. The thrustline distance target 62 projects upwardly away from the thrust linetarget base 66.

The user adjusts the position of the thrust line target 60 until thethrust line distance target 62 intersects the distance measuring line 53at the distance measuring line midpoint 53M. To ensure precise alignmentof the thrust line target 60, the thrust line distance target 62 mayhave a distance target alignment track 62T. The user ensures that thedistance measuring line 53 and the lateral alignment guide line 58remain aligned with the distance target alignment track 62T and thelateral target alignment track 64 respectively.

Turning to FIGS. 14 and 15 while also referring to FIG. 1A and FIG. 12,once the distance measuring line midpoint 53M has been located, thecenter visual guide projector 32 is positioned such that it is alignedwith the center guide line alignment mark 68. The center guide lineprojects the center guide line 70 perpendicularly to the lateralalignment guide line 58 and the distance measuring line 53. The centerguide line 70 is colinear with both the thrust line 50 of the vehicleand the vehicle center line 92, and is visible upon the horizontalsurface 100. In the example illustrated, the center visual guideprojector 32 can be placed on or above the horizontal surface 100, suchthat the center guide line 70 aligns with the center guide linealignment mark 68, thus ensuring that the center guide line 70 isperpendicular to the lateral alignment guide line 58. Alternatively, thecenter visual guide projector 32 may be positioned upon the thrust linetarget 60 in alignment with the center visual guide alignment mark 68 orthe thrust line distance target 62.

Referring to FIG. 16 and FIG. 17 while also referring to FIG. 1A, oncethe center guide line 70 has been projected onto the horizontal surface100, the calibration distance 51 for the sensor 94 is determined. In apreferred embodiment, a starting reference point 51A and an endingreference point 51B are located along either the first or secondlongitudinal guide lines 52L, 52R. In the example illustrated, the firstlongitudinal guide line 52L is used. The starting reference point 51Amay be aligned with the vehicle front 81F, the wheel center 88 of one ofthe front wheels 84, or any other suitable point in accordance with thecharacteristics of the sensor 94. The ending reference point 51B isseparated from the starting reference point 51A by the calibrationdistance 51.

The transverse visual guide projector 38 is positioned upon thehorizontal surface 100 along the first or second longitudinal guide line52L, 52R as appropriate. The transverse visual guide projector 38 isadapted to project the transverse guide line 56 across the horizontalsurface 100 such that it perpendicularly intersects the center guideline 70 at an intersection point aligned laterally with the endingreference point 51B. The intersection point corresponds to the optimumtarget position 72.

In one embodiment, the transverse visual guide projector 38 is a devicesimilar to a tile laser, and is adapted to project a transverseprojector alignment line 56L perpendicularly to the transverse guideline 56. By aligning the transverse projector alignment line 56L withthe first or second longitudinal guide line 52L, 52R, the transverseguide line 56 remains perpendicular to the center guide line 70 at theintersection point.

Referring to FIG. 18 and FIG. 19 while also referring to FIG. 17, thecalibration target 109 is placed upon the horizontal surface 100 at theoptimum target position 72 so that the vehicle center line 92 centrallyintersects the calibration target 109. Proper usage of the targetalignment system 10 ensures that the front and rear wheels 84, 85 arelongitudinally aligned, with the result that the thrust line 50 of thevehicle matches the vehicle center line 92 and there is no dangerousmismatch between the actual thrust line 50 of the vehicle 80 and anyperceived sensor data.

In one embodiment, the calibration target 109 has one or morecalibration marks 109M which serve as reference markers which aretracked by one or more sensing components 94B of the sensor 94. Correctplacement of the calibration target 109 ensures that the calibrationmarks 109M are accurately perceived by the sensing components 94B. Anattempt to calibrate the sensor 94 in which the calibration marks 109Mdeviate even slightly from the correct alignment with the vehicle centerline 92 results in an erroneous off-axis calibration 94C which iscompounded by distances between the vehicle and potential obstacles. Forexample, a calibration error of one degree can result in a seriousmismatch between the predicted path and the true path of the vehicle,whereby the ADAS of the vehicle 80 fails to predict a collision with adistant obstacle.

Turning to FIGS. 20A-20B while also referring to FIG. 1A and FIG. 18, toassist in calibrating a rear-facing sensor 95, the target alignmentsystem 10 may be utilized to locate a rear optimum target position 72Rfor the placement of a rear calibration target 109R. In a preferredembodiment, the first and second rear visual guide projectors 30C, 30Dare detached from the first and second rear wheels 85L, 85R followingthe successful calibration of the front-facing sensor 94. The first rearvisual guide projector 30C is instead reattached to the second rearwheel 85R, while the second rear visual guide projector 30D isreattached to the first rear wheel 85L. Both rear visual guideprojectors are oriented to project the first and second rear visualguide lines 54L, 54R rearwardly past the vehicle rear 81R. The first andsecond target assemblies 40L, 40R are placed to the rear of the vehicle80. The process for locating the rear optimum target position 109R issubstantially identical to the process for locating the optimum targetposition 109. However, the first and second longitudinal guide lines52L, 52R are omitted, and the first and second rear longitudinal lines54L, 54R are used instead to longitudinally align the first and secondtarget assemblies 40L, 40R respectively. Additionally, the transversevisual guide projector 38 is aligned with either the first or secondrear longitudinal guide lines 54L, 54R. The placement and usage of thelateral alignment visual guide projector 34, the distance measuringprojector 36, the thrust line target 60, the center visual guideprojector 32, and the transverse visual guide projector 56 is otherwisesubstantially the same as described above.

Due to the limited distances and slow speeds involved when reversing thevehicle, it is unnecessary to utilize all four wheel-mounted visualguide projectors 30. In one embodiment where the rear-facing sensor 95is a back-up camera, successful calibration may result in the rearthrust line 50R of the vehicle being matched with the vehicle centerline 92, such that when the vehicle 80 is placed in reverse, the actualpath 116 properly aligns with backup alignment indicators 114 displayedon the dashboard 118.

It is understood that when an element is referred hereinabove as being“on” another element, it can be directly on the other element orintervening elements may be present therebetween. In contrast, when anelement is referred to as being “directly on” another element, there areno intervening elements present.

Moreover, any components or materials can be formed from a same,structurally continuous piece or separately fabricated and connected.

It is further understood that, although ordinal terms, such as, “first,”“second,” “third,” are used herein to describe various elements,components, regions, layers and/or sections, these elements, components,regions, layers and/or sections should not be limited by these terms.These terms are only used to distinguish one element, component, region,layer or section from another element, component, region, layer orsection. Thus, “a first element,” “component,” “region,” “layer” or“section” discussed below could be termed a second element, component,region, layer or section without departing from the teachings herein.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper” and the like, are used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It is understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the example term “below” can encompass both anorientation of above and below. The device can be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly.

Example embodiments are described herein with reference to cross sectionillustrations that are schematic illustrations of idealized embodiments.As such, variations from the shapes of the illustrations as a result,for example, of manufacturing techniques and/or tolerances, are to beexpected. Thus, example embodiments described herein should not beconstrued as limited to the particular shapes of regions as illustratedherein, but are to include deviations in shapes that result, forexample, from manufacturing. For example, a region illustrated ordescribed as flat may, typically, have rough and/or nonlinear features.Moreover, sharp angles that are illustrated may be rounded. Thus, theregions illustrated in the figures are schematic in nature and theirshapes are not intended to illustrate the precise shape of a region andare not intended to limit the scope of the present claims.

In conclusion, herein is presented a target alignment system forcalibrating a vehicle-mounted safety sensor. The disclosure isillustrated by example in the drawing figures, and throughout thewritten description. It should be understood that numerous variationsare possible, while adhering to the inventive concept. Such variationsare contemplated as being a part of the present disclosure.

What is claimed is:
 1. A target alignment system for calibrating asafety sensor, the safety sensor is mounted upon a vehicle which ispositioned upon a horizontal surface, the vehicle having a vehiclefront, a vehicle first side, a vehicle second side, a vehicle rear, aplurality of wheels including a pair of front wheels, and a vehiclecenter line that extends longitudinally and centrally through thevehicle, the front wheels comprising a first front wheel at the vehiclefirst side and a second front wheel disposed at the vehicle second side,the safety sensor having a calibration target and an optimum targetposition in line with the vehicle center line upon which placement ofthe calibration target allows accurate calibration of the safety sensor,the optimum target position corresponding to a location upon thehorizontal surface, the target alignment system comprising: a pair oftarget alignment assemblies comprising a first target assembly and asecond target assembly, each target assembly having a target face and alateral target alignment track, the first and second target assembliesare positioned upon the horizontal surface ahead of the vehicle front,with the vehicle center line extending between the first and secondtarget assemblies; a plurality of wheel attachment assemblies, eachwheel attachment assembly has a visual guide attachment point and isdetachably secured to one of the front or rear wheels; a plurality ofwheel-mounted visible guide projectors comprising a first front visualguide projector and a second front visual guide projector, the firstfront visual guide projector and the second front visual guide projectorare each detachably secured to the first front wheel and the secondfront wheel respectively via the visual guide attachment point of one ofthe wheel attachment assemblies, the first front visual guide projectorand the second front visual guide projector are adapted to project afirst longitudinal guide line and a second longitudinal guide linerespectively on the horizontal surface, the first and secondlongitudinal guide lines are parallel with the vehicle central line andextend forwardly past the vehicle front, the first and secondlongitudinal guide lines align with the first and second targetassemblies respectively; a lateral alignment guide projector positionedon the first or second target assemblies, the lateral alignment guideprojector is adapted to project a lateral alignment guide line whichaligns with the lateral target alignment guides of both the first andsecond target assemblies and places the target assemblies in lateralalignment with each other; and a center visual guide projector adaptedto project a center guide line which is equidistant between the firstand second longitudinal guide lines, is colinear with the vehicle centerline, and which extends along the horizontal surface towards thevehicle, the center guide line allows the optimum target position to belocated upon the horizontal surface in line with the vehicle centerline.
 2. The target alignment system as described in claim 1, wherein:the first and second target assemblies each have a longitudinal targetalignment track which is oriented perpendicularly to the lateralalignment track, the longitudinal target alignment track of the firsttarget assembly is aligned with the first longitudinal guide line, andthe longitudinal target alignment track of the second target assembly isaligned with the second longitudinal guide line.
 3. The target alignmentsystem as described in claim 2, further comprising a thrust line targethaving a thrust line target lateral alignment track and a center guideline alignment mark oriented perpendicularly thereto, the thrust linetarget is placed on the horizontal surface with the thrust line lateralalignment track in alignment with the lateral alignment guide line andwith the center guide line alignment mark equidistant between the firstand second longitudinal guide lines, the center guide line alignmentmark allows the center guide line projected by the center visual guideline to align with the vehicle center line.
 4. The target alignmentsystem as described in claim 3, further comprising a transverse visualguide projector adapted to be aligned with a starting reference pointpositioned along either the first or second longitudinal guide line, thetransverse visual guide projector projects a transverse guide line uponthe horizontal surface which perpendicularly intersects the center guideline at an intersection point, the intersection point is separated fromthe starting reference point by a calibration distance, and visuallymarks the optimum target position.
 5. The target alignment system asdescribed in claim 4, wherein: the plurality of wheels further include afirst rear wheel and a second rear wheel disposed at the vehicle firstside and the vehicle second side respectively; the plurality ofwheel-mounted visual guide projectors further comprises a first rearvisual guide projector and a second rear visual guide projector, thefirst and second rear visual guide projectors are each attached to thefirst and second rear wheels respectively via the visual guideattachment point of one of the wheel attachment assemblies, the firstand second rear visual guide projectors are adapted to forwardly projecta first rear longitudinal guide line and a second rear longitudinalguide line to converge with the first and second longitudinal guidelines upon the horizontal surface, whereby convergence of the firstlongitudinal guide line and the first rear longitudinal guide lineindicates longitudinal alignment of the first front and first rearwheels, and convergence of the second longitudinal guide line and thesecond rear longitudinal guide line indicates longitudinal alignment ofthe second front and second rear wheels.
 6. The target alignment systemas described in claim 5, wherein: the longitudinal target alignmenttrack of each target assembly further has a horizontal component whichprojects horizontally and perpendicularly away from the target face, anda vertical component which extends upwardly and perpendicularly awayfrom the horizontal surface; the first longitudinal guide line and thesecond longitudinal guide line each form a first vertical guide line anda second vertical guide line respectively upon intersecting the verticalcomponent of one of the longitudinal target alignment tracks, and thefirst longitudinal guide line and the second longitudinal guide lineeach form a first rear vertical guide line and a second rear verticalguide line respectively upon intersecting the vertical component of oneof the longitudinal target alignment tracks; whereby the first targetassembly is longitudinally aligned by converging the first longitudinalguide line and the first rear longitudinal guide line with thehorizontal component of the first target assembly, and the second targetassembly is longitudinally aligned by converging the second longitudinalguide line and the second rear longitudinal guide line with thehorizontal component of the second target assembly; and whereby thefirst target assembly is leveled in relation to the horizontal surfaceby aligning the first vertical guide line and the first rear verticalguide line with the vertical component of the first target assembly, andthe second target assembly is leveled in relation to the horizontalsurface by aligning the second vertical guide line and the second rearvertical guide line with the vertical component of the second targetassembly.
 7. The target alignment system as described in claim 6,wherein: the first front visual guide projector and the first rearvisual guide projector are adapted to project a first horizontal guideline and a first rear horizontal guide line respectively upon the targetface of the first target assembly, and the second front visual guideprojector and the second rear visual guide projector are adapted toproject a second horizontal guide line and a second rear horizontalguide line respectively upon the target face of the second targetassembly; and whereby the first front wheel is level with the first rearwheel upon the horizontal surface when the first horizonal guide line ishorizontally aligned with the first rear horizontal guide line upon thetarget face of the first target assembly, and the second front wheel islevel with the second rear wheel upon the horizontal surface when thesecond horizonal guide line is horizontally aligned with the second rearhorizontal guide line upon the target face of the second targetassembly.
 8. The target alignment system as described in claim 7,further comprising a distance measuring projector positioned upon eitherthe first target assembly or the second target assembly and a distancetarget positioned upon the opposite target assembly, the distancemeasuring projector is adapted to project a distance measuring line tothe distance target to determine a distance between the first and secondlongitudinal guide lines, the distance measuring line being parallelwith the lateral alignment guide line; and the thrust line target has athrust line distance target longitudinally aligned with the center guideline alignment mark, and the thrust line target is placed upon thehorizontal surface such that the thrust line distance target intersectsthe distance measuring line at a distance measuring line midpoint whichis equidistant between the first and second longitudinal guide lines. 9.The target alignment system as described in claim 8, wherein thetransverse visual guide projector is further adapted to project atransverse projector alignment line perpendicularly away from thetransverse guide line, the transverse guide line is maintained inperpendicular alignment with the first or second longitudinal guide lineby aligning the transverse projector alignment line with the first orsecond longitudinal line.
 10. A method for calibrating a safety sensormounted upon a vehicle, the vehicle having a vehicle front, a vehiclefirst side, a vehicle second side, a vehicle rear, a pair of frontwheels and a pair of rear wheels, and a vehicle center line that extendslongitudinally and centrally through the vehicle, the front wheelscomprising a first front wheel disposed at the vehicle first side and asecond front wheel disposed at the vehicle second side, the rear wheelscomprising a first rear wheel disposed at the vehicle first side and asecond rear wheel disposed at the vehicle second side, the vehiclehaving a thrust line corresponding to a direction of travel determinedby the front and rear wheels, the method comprising the steps of:providing a pair of target assemblies including a first target assemblyand a second target assembly; providing a plurality of wheel-mountedvisible guide projectors comprising a first front visual guide projectorand a second front visual guide projector; providing a lateral guideline projector and a center guide line projector; providing acalibration target for calibrating the safety sensor; positioning thevehicle upon a horizontal surface; attaching the first front visualguide projector and the second front visual guide projector to the firstfront wheel and the second front wheel; placing the first and secondtarget assemblies upon the horizontal surface ahead of the vehiclefront; forming a visible guide line perimeter around the vehicle byprojecting a first longitudinal guide on the horizontal surface alongthe vehicle first side using the first front visual guide projector,projecting a second longitudinal guide line on the horizonal surfacealong the vehicle second side using the second front visual guideprojector, aligning the first target assembly with the firstlongitudinal guide line, aligning the second target assembly with thesecond longitudinal guide line, and projecting a lateral guide line uponthe horizontal surface between the first and second target assembliesusing the lateral guide line projector which perpendicularly crosseseither the first or the second longitudinal guide lines, positioning thecenter guide line projector between the first and second targetassemblies, projecting a center guide line upon the horizontal surfacewhich is colinear with the vehicle center line using the center guideline projector, the center guide line perpendicularly intersecting thelateral guide line at a midpoint equidistant between the first andsecond longitudinal lines; locating an optimum target position along thecenter guide line; and placing the calibration target upon the optimumtarget position, and initiating a calibration procedure by which thesafety sensor is accurately calibrated.
 11. The method as recited inclaim 10, wherein: the step of positioning the vehicle upon a horizontalsurface further is preceded by the step of providing a transverse guideline projector; and the step of locating an optimum target positionfurther comprises selecting either the first or the second longitudinalguide lines and designating a starting reference point along theselected longitudinal guide line, measuring a calibration distance fromthe starting reference point to locate an ending reference point alongthe selected longitudinal guide line, projecting a transverse guide lineupon the horizontal surface using the transverse guide line projectorwhich aligns with the ending reference point and perpendicularlyintersects the center guide line to mark the optimum target position.12. The method as recited in claim 11, wherein: the plurality ofwheel-mounted visible guide projectors further comprise a first rearvisual guide projector and a second rear visual guide projector; and thestep of forming a visible guide line perimeter around the vehiclefurther comprises projecting a first rear longitudinal guide line on thehorizontal surface along the vehicle first side using the first rearvisual guide projector, and projecting a second rear longitudinal guideline on the horizontal surface along the vehicle second side using thesecond rear visual guide projector.
 13. The method as recited in claim12, wherein the step of positioning the center guide line projector isfollowed by the step of: confirming that the thrust line of the vehiclematches the center guide line by longitudinally aligning the first rearwheel with the first front wheel by placing the first rear longitudinalguide line in alignment with the first longitudinal guide line to form acolinear first convergence, and longitudinally aligning the second rearwheel with the second front wheel by placing the second rearlongitudinal guide line in alignment with the second longitudinal guideline to form a colinear second convergence.
 14. The method as recited inclaim 13, wherein: the step of providing a lateral guide line projectorfurther comprises providing a thrust line target having a thrust linetarget lateral alignment track and a center guide line alignment markoriented perpendicularly thereto; the step of forming a visible guideline perimeter is followed by the step of placing the thrust line targetupon the horizontal surface between the first and second targetassemblies, aligning the thrust line target lateral alignment track withthe lateral alignment guide line while positioning the center guide linealignment mark equidistant between the first and second longitudinalguide lines; and the step of positioning the center guide line projectorfurther comprises projecting a center guide line upon the horizontalsurface which aligns with the center guide line alignment mark of thethrust line target and is colinear with the vehicle center line usingthe center guide line projector.
 15. The method as recited in claim 14,wherein each target assembly has a target face, the front wheels and therear wheels each have a wheel center and the step of forming a visibleguide line perimeter is followed by the steps of: projecting a firsthorizontal guide line and a first rear horizontal guide line upon thetarget face of the first target assembly using the first front visualguide projector and the first rear visual guide projector respectively,whereby the first horizontal guide line passes through the wheel centerof the first front wheel and the first rear horizontal guide line passesthrough the wheel center of the first rear wheel; projecting a secondhorizontal guide line and a second rear horizontal guide line upon thetarget face of the second target assembly using the first front visualguide projector and the first rear visual guide projector respectively,whereby the second horizontal guide line passes through the wheel centerof the second front wheel and the second rear horizontal guide linepasses through the wheel center of the second rear wheel; placing thewheel centers of the first front wheel and the first rear wheel inhorizontally coplanar alignment by aligning the first horizontal guideline and the first rear horizontal guide line upon the target face ofthe first target assembly; and placing the wheel centers of the secondfront wheel and the second rear wheel in horizontally coplanar alignmentby aligning the second horizontal guide line and the second rearhorizontal guide line upon the target face of the second targetassembly.
 16. The method as recited in claim 15, wherein the step ofplacing the wheel centers of the second front wheel and the second rearwheel in horizontally coplanar alignment is followed by the step of:adapting to irregularities upon the horizontal surface affecting thehorizontal coplanar alignment of the front and rear wheels by insertinga leveling shim under one or more of the wheels.